The present invention relates to a color photographic material and more particularly it relates to a color photographic material wherein a nondiffusing oil soluble color coupler is stably dispersed in an aqueous protective colloid layer containing silver halide emulsion in oil-in-water state and stability of color images formed by color development of the coupler is improved.
It has been known in U.S. Pat. No. 2,322,027 (1943) that nondiffusing oil soluble coupler is dissolved in a high boiling point organic solvent such as dibutyl phthalate (DBP) or tricresyl phosphate (TCP), thereafter the solution is emulsified and dispersed in an aqueous protective colloid material such as gelatin in oil-in-water state in the presence of a surfactant by colloid mill or homo mixer and the resultant dispersion is added to an aqueous protective colloid such as gelatin which contains silver halide, whereby the dispersion is introduced into color photographic material in finely dispersed non-crystalline or nearly non-crystalline state.
The high boiling point organic solvents used in said method not only possess direct photographic function, but also are apt to damage permeability of developers and moreover to deteriorate properties of emulsion layer. Therefore, content of these solvents in film layers is desirably as small as possible. Therefore, it is necessary that they have sufficiently high solubility for couplers. Furthermore, practical ratio of coupler and the high boiling point organic solvent is about 1 : 1 - 1 : 3 while solubility of coupler is usually considerably lower than said ratio and so at said ratio the coupler dispersion is generally in supersaturated state. Therefore, it is necessary requirements that not only the solvents have high solubility, but also they are high in supersaturation stability. When these requirements are insufficiently met, extra amount of solvent is required. Thus, thickness of coated film layer is increased to result in increased tendency of curling up of photographic materials, reduction in permeability of developer and color forming efficiency in color development, decrease in sharpness of image due to scattering of light in film layer and brightness of color and increase in production cost.
Other requirements to be possessed by high boiling point organic solvents used for this purpose are that the solvents per se have no color, they have good compatibility with medium incorporated therein, they are inert to other additives in photographic material and treating solutions, they cause no photographic fogging and have no effect on sensitivity and gradation.
Still other requirement is that stability of dye produced by reaction of a coupler with an oxidized color developer against ultraviolet ray and wet heat is high. For stabilizing against ultraviolet ray, selection of the high boiling point organic solvents is useful, but practically sufficient stabilization effect can be obtained by providing a filter layer which uses commonly employed ultraviolet absorbers such as 2-arylbenzotriazole and benzophenone type ultraviolet absorbers. However, stability against humidity and heat depends greatly upon the high boiling point organic solvents used. Thus, search for such organic solvents has been intensively conducted.
Furthermore, as mentioned above, in order to prevent dyes in color images from fading due to ultraviolet ray, ultraviolet ray absorbing filter layer is usually provided and it is well known that 2-aryl-benzotriazole derivatives are particularly effective for this purpose. The 2-aryl-benzotriazole derivatives per se are excellent in light and heat stabilities to cause no decomposition and no undesired coloration. Furthermore, they are colorless and effectively intercept the ultraviolet ray of a spectrum of 300 - 400 nm and effectively transmit a light of more than 400 nm.
As in the case of couplers mentioned hereinbefore, in order to introduce said 2-aryl-benzotriazole derivative into color photographic materials as ultraviolet ray filter layer, conventionally the derivative is dispersed in non-crystalline form as oil-in-water droplets dissolved in a high boiling point organic solvent such as dibutyl phthalate or tricresyl phosphate. Such method is disclosed in Japanese Patent Publications No. 26,178/67 and No. 29,620/69.
The greatest difficulty in introduction of 2-arylbenzotriazole ultraviolet ray absorber into layers of color photographic materials is that said compound is extremely liable to crystallize. Crystallization of 2-aryl-benzotriazole derivative in oil droplets brings about troubles such as ununiform coating in production of photographic materials, damage of surface gloss of film or opacification of the film and reduction in absorbing ability of ultraviolet ray as compared with the case where 2-arylbenzotriazole derivative is dispersed in non-crystalline form. This crystallization may occur not only in production of photographic materials, but also in storage of the materials, in treating step such as development and furthermore after lapse of time from the treatment.
The high boiling point organic solvent used herein must high solubility for 2-arylbenzotriazole derivative. If the solubility is insufficient, such disadvantages as explained hereinbefore with reference to the solvent for couplers also occur.
In order to compensate the insufficient solubility and to make the size of the dispersed oil particles finer, low boiling point organic solvents such as ethyl acetate, isopropyl acetate, cyclohexane, etc. may be jointly used as an assistant solvent to attain emulsification and dispersion. However, due to evaporation of the assistant solvent, density of the ultraviolet absorber in the oil particles is increased to cause instabilization of the dispersed particles and to result in easy crystallization.